Aircraft landing gear with means for minimizing wheel drag load incident to landing



Feb- 23, 1954 c. B. v. NElLsoN E1- AL 2,670,160

AIRCRAFT LANDING GEAR WITH MEANS FOR MINIMIZING WHEEL DRAG LOAD INCIDENT TO LANDING Filed April 17, 1950 v I N VEN TORS Chr-sicpkerermrd Vere/wilson Patented Feb. 23, 1954 AIRCRAFT LANDIN G GEAR WITH MEANS EOR MINIMIZING WHEEL DRAG LOAD INCIDENT T0 LANDING Christopher Bernard Vere near Warrington, Warrington,

Neilson, Fearnhead,

and Robert George Hoare, England, assignors to Electro- Hydraulics Limited, Warrington, England, a company of Great Britain Application April 17,v 1950, Serial No. 156,246

Claims priority, application July 14, 1949 5 Claims.

This application is a continuation-impart of 'the copending application of Christopher Ber- -nard` Vere Neilson and Robert George Hoare,

Serial No. 48,466, led September 9, 1948, now abandoned. 1

This invention relates to aircraft landing gear,

and more particularly to improvements in the construction of such gear by which drag loads incident to landing are minimized. l Modern aircraft, particularly large and heavy airplanes, commonly are equipped with landing gear vcomprising closely associated sets of wheels grouped in a unit and spaced from each other foreand-aft, that is in the direction of the line y01' night. customarily the wheels of such a set or unity are mounted on the undercarriage leg or other support in such manner, or at such an angle tothe ground during a landing approach, that the leading and trailingr wheels of the set, group, orV unit of tandem wheels contact the ground simultaneously. Since the `wheels normally are not rotating at the time of initial contact with the ground, their static inertia (to rotation) must be overcome to start them rotating, resulting in a serious drag which produces some tendency for the aircraft to nose over.

Various proposals have heretofore been put forward to overcome these disadvantages, for example by providing the landing wheels or tires with flaps operating by the air ow to spin up or start the wheelsrotating before landing. Such arrangements, however, are subject to the disadvantage that they increase wind resistance. It also has been proposed to provide special motors for spinning up the wheels justvbefore landing; but the penalties of increased weight, cost, and complexity of the contact equipment attending -such expedients are apparent. l V An object of the present invention is to provide an aircraft landing gear construction in which relatively rotatable tandem wheels cf a set of fore-and-aft spaced wheels are normally -vso biassed that when the aircraft approaches the ground for a landing one of the wheels is lower s than its associated tandem wheel, the arrangement being such that the lower wheel contacts the ground rst and is started to rotate, after which the biassing means enables the other wheel vto move downwardly, relatively to the aircraft. y to contact the ground and to be started to rotate.

In this way the drag loads resulting from overy coming inertia'of the two wheels are imposedjin 'successi'omrather than simultaneously; and fthe :maximum instantaneous dragload is greatlyvreload which is hard on L vthe landing wheel tires, and

Great Britain duced. A related advantage of constructionsembodying the present invention is that the reduction in maximum drag loads permits most, if not all, parts of the undercarriage to be more lightly constructed. v

An inportant requirement of the present invention is that the tandem wheels of a unitor set be freely relatively rotatable as well as that they be mounted and biassed so as to eect the successive ground contact and spinning up referred to above. Accordingly the invention is not adapted for use in landing gear constructions ofthe endless band type inv which not only must the whole band be started to move at one time, but also the wheels mounting the band must simultaneously be started to rotate, thus aggravating the disadvantages due to overcoming the static inertia of a plurality of wheels.. 1

A representative embodiment of the invention is illustrated in the accompanying drawings. in which:

Figure 1 is a somewhat diagrammatic elevation of an aircraft undercarriage support or leg on which mechanism embodying the invention is mounted, the parts being shown in the positions occupied before thewheels are loaded; and

Figure 2 is a View similar to Figure 1 but showing the parts in the positions occupied when the wheels are loaded.

In each of the gures, the line of flight may, for convenience, be considered as being indicated by the arrow The construction shown in Figure 1 includes an undercarriage support or leg, generally designated I, adapted to be connected at its upper end to an aircraft in any suitable manner. The support l is shown as including a cylinder element Zand a piston element or sliding tube 3. `Mounted on the lower end of theA piston element 3 is a iitting Ll fast to which is an arm 3l offset from the center line of the leg I forwardly in the direction ci the line of iiight. vPivoted at 3S on the arm-'3| is a bogie or truck frame 29 which is adapted to tilt about the pivot 30. ending wheels l and arranged substantially in tandem or fore-and-aft disposition are-journalled, respectively, at il and I0 on the leading and trailing ends of the bogie 29. Any suitable means may be provided. for holding the bogie and the wheels aligned in the direction of the line of flight. In the form shown, thel aligning means includes a pair of toggle links Il and l2 pivoted together at I3,V andpivoted respectively at rI4 and I5 to the fitting 4 andfto the cylinder' element 2. f i

In accordancewth the invention, thebogie 29 is so biassed thaw-when the supporti is in the position it normally occupies when the aircraft is approaching a landing, one of the landing wheels will be disposed lower than the construction shown in Figureohzthe'bogiel the other. In`

' Lal' is so biassed that the trailingwheela isdisposed f lower than the leading wheel 1. The oushion- Y ing or biassing device for.normaily,holdingthe bogie 29 tilted so as to disposev the trailingV wheel 8 lower than the leading wheellmay be a shock absorber device functioning dually-.as theshockabsorber for the landing-wheels and as means' for biassing the rear wheel or rear wheels of the bogie downwardly when air-borne 'or on yland- In this case, the shoclt.-absorber.isfixed ing.

against vertical movement in the telescopicrleg on its upper end only, whereas the lower end of the shock absorber isfree to slide in the' telescopic leg. 4routerrcylinderr 2 andlthe' 'innerscylinder or slid- -ingntubelf The shock absorber consistsA of the outer .cylinderf33 and.' the inner concentric cylinfderlor pistons??` providing. aA cushioning member.

The shock absorber may be of the general" class .ingiwheel,'r"lcntacts'the'groundir The'piston 32 will yield upwardly when the vertical load isim- 'posed on theitrailing wheel 8 so as topermit the bogi'e r2E! to tilt and bringthe' leading wheel 'l Iintof `contactwith the ground as shown in Figure-:2: fl'hus" wheels'f and l `are sp-'un up in lsuccession;` 'Ihrst' part of the-closureof the -main Shock-absorber `will'be accomplished withfoutlclosurevfof the telescopic'cylinders lZand 3, while the second and larger part of the closure -f'offtheishock absorber will be accomplished by fa corresponding closure of cylinders- 2 `andi The construction disclosed embodies" thein- 'vention in preferred form, butiiitis` intended that4`v the disclosure -be illustrative rather` than "definitive *of the invention, and-maybe particu- 'larly adapted to bogies'carrying more than two 'wheelsf'in tandem, or more than one pair of wheelsuntandem,` orexample, 'two pairs of 'whee'ls in tandem, one on each sideof the frame 29,"the invention being defined in the claims.

,We'olaimtl 1; In aircraft llanding gear construction, an undercarriage support; a bogie; two landing wheels journalled on said bogie for independent :relative-rotation and spacedfore-and-aft of each other so that-one is leading and oneV is trailing "-viithrespect totheline of flight; means mounting'vsaid-bogie on `said support for tilting about -an -axis transverse to the line of night; and

'yield'a'ble-means biassingsaid bogie toa position lin which'one of said wheels is lower than the "other of said-wheels when said support is at the normal JA landing approach angl'evto the ground, wherebyfsaidelower whe-el (will beY rotated by contact with the ground before the other.` of said.

The telescopic leg consists of the Eli ' journalled' on wheels contacts the gronndsaid .mounting means f comprising ai vertically:imovar'ble` pistoni element and a pivotal connection between said bogie and said element, said biassing means comprising a cushioning member mounted for vertical movelment, a link,-,;avpivotal connection between one endof` saidrlink and said cushioning member and a pivotal vconnection between the other end of said link and said bogie, said piston element and saidicushioningmember being constituted of reciprocablelconcentric pistons, one within the others- 2. In-aircraftlanding gear construction, an undercarriage support, a bogie, two landing wheels` journ'alledon said bogie for independent relativerotationand spaced fore-and-aft of each other so that one is leading and one is trailing with respect to the line of flight, said support including" a shock absorber disposed longitudinally of and within the support, said shock absorber havingsaazpiston; means :mounting: said bog'ie 'fonvsaidz piston-.1y for' tilting Iabout z an axis transverse :to thea 'line of n flight, said; shockzabsorber:biassing` 'saidlfxigie :to a position in which one of said wheels is lower than thevotherfof said wheels whenisaidrsupportis at the normal landingv approach@ angie to the :1 ground; 4whereby saidlower wheel will 'berotated by contact'with the ground beforeI the: otherrofj said wheelscontacts the ground; said/'shock absorber .beingof a capa-city 'to delay'contactof'saidiother wheeliwith thexground "until thelsaid4` lower-'wheel rotates by contact with ,thegroundzir l3. In 'aircraft f landing; :gear rconstruction', an undercarriage leg ihavingta cylinder and a'jtube slidable; therein; a' shock absorben'havingpa: cylinder xed within the'first.: cylinder; a s piston within said tube slidablein the"A second-.mentioned cylinderf and;coactingfztherewith"to form a shock'absorber, abogie; two "landing wheels said; bogie 'forz independent-relative rotation rand spaced'A fore-and-aftrof each other so that oneisleadingand one is: trailing `witlfrrespect' to the line of'ight'means mounting said bogie on saidl tube for-tilting 'abouti an axis -transverse to the` line of flight;` :linkage through thelower i end of saidf tube-'connecting said/piston4 and said bogie,saidishock'absorber biass'i'ng' said" bogie to a position' in whichoone of said wheels is lower' thany the 'other' of'said wheels: when said ileg" is at thenormali landing approach angle -to i the! ground,1whereby said-lower `Wheel -lwillfbe rotated by contact* with' the ground' before the otherof said wheelsl contacts the-'.grourrd,said-shock absorberrbeingof a capacityy to' delay-contact of saidvother Awheelywith 'the "ground until the said lower wheel rotatesfby conta'ctfwith thefground.

4. In aircraft landing'egear; a leghavingiacylinderf` a tube' member :slidable n therein, Ia bogie,

Ytwo ylandingf-wheels journalledon said :bogie lfor independent' relative rotation and spaced `fore-- and-aft of each other-so that one is leadingand one is trailing: with respect` to the lineiof ight, 'a shock absorber.; including -az cylinder: Xedz'lin thexfirst cylinderfandai piston Imeinbert within thetube. slidable'within .the second-,mentioned cylinder;A linkage connecting said; bugie: to one of said; members f whereby f ythe-gv shockv :absorber lbiasses said bogie to f af tposition 'in which one yof said' wheels isrlower than theotherrof said: wheels when nsaid legis atv the normal landing approach angie; to,` thee-ground, whereby'- saidrlowerfwheel willfloe' rotatedzby contactwith `thegronnidbefore thes-fothen of saidf,wheelsrcontactsz:the gronnl,

said shock absorber being of a capacity to delay contact of said other wheel with the ground until the said lower wheel rotates by contact with the ground.

5. In aircraft landing gear construction, an undercarriage support comprising a cylinder; a bogie; two landing wheels journalled on said bogie for independent relative rotation and spaced fore-and-aft of each other so that one is leading and one is trailing With respect to the line of vflight; a piston element reciprocable in said cylinder and mounting said bogie on said support for tilting about an axis transverse to the line of ight; and yieldable means biassing said bogie to a position in which one of said wheels is lower than the other of said wheels when said support is at the normal landing approach angle to the ground, whereby said lower wheel will be rotated by contact with the ground before the other of said wheels contacts the ground, said biassing means comprising a shock absorber also having relatively longitudinally movable piston and cylinder elements, the said two piston elements being in concentric nested relation.

CHRISTOPHER BERNARD VERE NEILSON. ROBERT GEORGE HOARE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,379,576 Killen May 24, 1921 1,653,361 Krammer Dec. 20, 1927 1,802,692 Zindel Apr. 28, 1931 2,433,830 DoWty Jan. 6, 1948 2,490,485 Spaeth Dec. 6, 1949 FOREIGN PATENTS Number Country Date 123,174 Great Britain Feb. 18, 1919 537,541 Great Britain June 26, 1941 

